Such gear selectors, in which the driver or an electronic device merely selects the gear, and the gear change is performed in the gearbox proper by a servo-assisted actuating device rather than directly by the driver via a shifting linkage, have been known in many designs, e.g.,
ZF [Zahnradfabrik Friedrichshafen AG ] Specification for electropneumatic selection (ES) for synchromesh transmissions F 43546/RT 3430-885, PA1 ZF specifications for automated preselector (APS) for synchromesh transmissions F 32437/RT 3431-885. PA1 electronic-pneumatic selector EPS for trucks of Daimler Benz Aktiengesellschaft, Order No. 6510302300 of March 1986, PA1 Scania - Leichter schalten mit Computer (Shift more easily by a Computer), page 4, column 2, paragraph 2.
In all these designs, the clutch and consequently the drive train between the engine and the gearbox is disengaged and engaged, as before, by the driver via the clutch pedal by the driver. While in the case of gear selection via a shifting linkage, the driver recognizes when the gear has been selected as a consequence of the direct contact with the shifting means in the gearbox, this information, which is generated in conjunction with the actuation of the gear shift lever and the shifting linkage, is lacking in the case of a servo-assisted gear selector. To ensure properly timed actuation of the clutch, especially for engaging the clutch after completion of the selection in the gearbox, a corresponding feedback must be generated in order to again engage the drive train disengaged via the clutch shortly after completion of the selection process in the gearbox.
It is known from the first-mentioned ZF publication for an electropneumatic selector (ES) that the corresponding gear can be selected with the lever of the gear selector. A noticeable restoring force acts against the selection movement, and this force is abolished as soon as the gear selected in the gearbox is thrown in. The lever can now be moved easily into the end position. This also represents a signal for re-engagement for the driver.
In the automated preselector (APS) according to the second ZF publication, the feedback on completion of the selection is an acoustic feedback generated by a buzzer, page 2, column 2, paragraph 1. This also represents the signal for re-engagement for the driver. According to the EPS Manual on trucks of Daimler Benz Aktiengesellschaft, page 8, the selection is complete only when the gear shift lever can be moved farther out of a looked preselected position into position 2, which is present in each direction of shifting. The clutch pedal and the gear shift lever can be released only when the gear selected is shown in the display.
It is recognizable from the Scania brochure titled "Leichter Schalten mit Computern" (Shift more easily by a Computer), page 4, paragraph 1, that a buzzing tone signals to the driver when the selection process is complete and the clutch can be released.
Even though the connection of the feedback for the selection performed in the gearbox to the gear shift lever does provide the driver with information, which comes closest to the information from a gear selector with a shifting linkage, it is bound, as is shown by the examples presented, to the gear shift lever or a comparable gear shifting lever, and involves high cost of construction.
Even though an acoustic signal can be easily realized, it is not particularly suitable as information for the driver, and such signals are burdensome in the case of frequent gear shiftings. In addition, acoustic signals are used as warning signals, whereas the feedback on the selection in a gearbox represents a perfectly normal, but necessary piece of information in the case of servo-assisted selection.